An adjustable friction device for retarding the castering movement of a support wheel for a plow is shown in U.S. Pat. No. 3,488,064 issued to R. G. Moe on Jan. 6, 1970 for an Implement Caster Wheel. An implement with front and rear castered wheels for supporting a ground working implement wherein the front wheels are locked in the lowered position of the implement is shown in U.S. Pat. No. 3,633,679. U.S. Pat. Nos. 2,843,948 and 3,701,385 show a castered wheel for an earthworking implement wherein the castered wheel is locked in the raised transport position of the implement. Agricultural implements with castered wheels which are locked in the lowered position of the implement are shown in U.S. Pat. Nos. 1,489,467; 1,598,803; 1,865,598; 2,682,822; 2,824,505; 3,106,971 and 3,448,815.